Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Cash flows from operating activities:
Net loss	$ (360,228)	$ (261,120)
Adjustments to reconcile net loss to net cash used in operating activities:
Change in fair value of contingent consideration	510	796
Depreciation and amortization	7,831	8,199
Stock-based compensation expense	87,452	51,051
Unrealized loss on equity securities	6,184
Other non-cash items	(7,064)	2,834
Changes in operating assets and liabilities:
Prepaid expenses and other assets	(20,694)	(3,279)
Operating lease right-of-use assets	11,037
Accounts payable	6,652	4,097
Accrued expenses and other liabilities	(9,301)	9,789
Operating lease liabilities	(259)
Deferred revenue	(11,716)	(21,589)
Collaboration research advancement	(2,431)
Net cash used in operating activities	(292,027)	(209,222)
Cash flows from investing activities:
Purchase of property, plant and equipment	(37,925)	(20,689)
Purchases of marketable securities	(471,365)	(689,163)
Proceeds from maturities of marketable securities	704,803	417,640
Net cash provided by (used in) investing activities	195,513	(292,212)
Cash flows from financing activities:
Proceeds from public offering of common stock, net of issuance costs		48,702
Reimbursement of assets under financing lease obligation		3,098
Payments on financing lease obligation		(446)
Proceeds from exercise of stock options and ESPP contributions	15,004	25,624
Net cash provided by financing activities	15,004	76,978
Decrease in cash, cash equivalents and restricted cash	(81,510)	(424,456)
Cash, cash equivalents and restricted cash at beginning of period	417,099	772,268
Cash, cash equivalents and restricted cash at end of period	335,589	347,812
Reconciliation of cash, cash equivalents and restricted cash:
Cash and cash equivalents			$ 280,995	$ 333,949
Restricted cash included in receivables and other current assets			$ 100	$ 100
Restricted Cash, Current, Asset, Statement of Financial Position [Extensible List]			blue:ReceivablesAndOtherCurrentAssets	blue:ReceivablesAndOtherCurrentAssets
Restricted cash included in restricted cash and other non-current assets			$ 54,494	$ 13,763
Restricted Cash, Noncurrent, Asset, Statement of Financial Position [Extensible List]			us-gaap:OtherAssetsNoncurrent	us-gaap:OtherAssetsNoncurrent
Total cash, cash equivalents and restricted cash	417,099	772,268	$ 335,589	$ 347,812
Supplemental cash flow disclosures from investing and financing activities:
Purchases of property, plant and equipment included in accounts payable and accrued expenses	8,869	$ 7,815
Assets acquired under operating lease obligation	$ 17,489